1. Field of the invention
The present invention concerns a torsional damper comprising at least two coaxial parts mounted to rotate relative to one another within a defined range of relative angular movement and circumferentially acting elastic means resisting such relative angular movement.
2. Description of the prior art
This type of torsional damper is normally incorporated in the design of a friction clutch, particularly for automotive vehicles, in which case one coaxial part comprises a friction disk designed to rotate with a first shaft, in practice a driving shaft and the motor output shaft in the case of an automotive vehicle, whereas another of said coaxial parts is carried on a hub designed to rotate with a second shaft, in practice a driven shaft and the gearbox input shaft in the case of an automotive vehicle.
This type of device is used to permit regulated transmission of rotational torque applied to one of its coaxial parts where the other is itself subject to a rotational torque. It is thereby able to filter vibrations which may arise at any point in the kinematic system in which it is incorporated, extending from the motor to the driven road wheels in the case of an automotive vehicle.
The circumferentially acting elastic means usually comprise only helical springs, each disposed substantially tangentially relative to a circumference of the damper assembly. Each individual spring is housed partly in an opening formed in an annular member constituting part of one of the coaxial parts, such as a transversely disposed disk or flange, for example, and partly in an opening formed in a parallel component constituting part of the other of said coaxial parts, in the form of a ring, for example.
The housing of these springs in the respective components raises serious problems in that forming the necessary openings reduces their mechanical strength.
In view of the minimum mechanical strength to be achieved and the generally limited spaced available, as measured in the radial direction, generally ruling out the installation of springs on two separate concentric circumferences of the damper assembly, there is frequently an upper limit in respect of the number of springs which may be used with corresponding limitations in respect of at least some of the operating characteristics of the torsional damper.
It has alreay been proposed to use at least one elastically deformable arm as the circumferentially acting elastic means in order to overcome this difficulty.
In U.S. Pat. No. 2,114,247 all the circumferentially acting elastic means comprise elastically deformable arms, of which there are two, one acting when the transmitted torque is increasing and the other when it is decreasing.
Each of the elastically deformable arms disclosed in this U.S. Patent is formed by helically winding a bar which is substantially square in transverse cross-section. The helical winding is difficult to achieve in practice. The elastically deformable arm extends from one end, in practice its inner end, shaped as a right-angle bracket and attached radially to one of the rotating parts of the torsional damper, to a second end, in practice its outer end formed as a hook which connects it to the second of said rotating parts.
Thus at one of its ends at least, in this instance its inner end, this kind of elastically deformable arm is attached by means of a flanged connection so that in operation the resulting deformation of the arm leads to problems of binding and of wear in the corresponding engagement area.
At its other end, in this instance the outer end at which it is coupled to one of the rotating parts of the torsional damper, there are problems of binding and wear in operation as the contact whereby this end is coupled to said rotating part is a pivoting one and therefore subject to friction.
In French Pat. No. 1423139 the circumferentially acting elastic means are only partially constituted by an elastically deformable arm.
This elastically deformable arm is cut out from a thin plate which is disposed transversely and whose thickness in transverse cross-section and in the axial direction is small in comparison with its dimension in the radial direction, so that the space required for the arm in the axial direction is minimal.
In French Pat. No. 1423139, however, the elastically deformable arm is coupled to the two rotating parts between which it is disposed by means of pivots so that, as with the previous disclosure, there are problems of binding and wear at these pivots in operation.
The object of the present invention is to provide an arrangement which overcomes these disadvantages and also offers further advantages.